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Verification of agricultural emissions at local scale: pilot project to develop approach and provide CH4 emission estimates. - AC0124

Description
Summary
Agriculture is currently estimated to contribute ~8% total UK greenhouse gas (GHG) emissions. The sector’s main contribution (~7%) to the inventory is through emissions of nitrous oxide (N2O) and methane (CH4), with carbon dioxide (CO2) responsible for ~1%. The 2008 UK GHG inventory attributes 75% of N2O and 37% of CH4 emissions to agriculture. These emissions are primarily from (i) enteric fermentation in livestock (methane); (ii) the use of nitrogen in agricultural soils (nitrous oxide); and (iii) agricultural manure management (methane and nitrous oxide).

The current inventory uses a simple, bottom-up approach to inventory construction which is based on scaling up animal and field-scale emissions studies. The approach used is best practice, but even so large uncertainties are involved and additionally the approach does not adequately reflect mitigation practices. DEFRA is currently supporting a new research programme to provide improved inventories of CH4 and N2O in order to address these uncertainties.

At present, no method exists to verify the accuracy of such inventories at anything close to farm scale, though techniques based on atmospheric measurements of the GHG have been developed to provide estimates of national and regional emissions, i.e. with spatial resolution of 100s of km square. Further, these techniques tend to produce either annual averages or instantaneous estimates which do not allow any detailed diagnosis of why any discrepancies might arise between the bottom-up and top-down estimates. This project aims to fill this gap by developing a technique capable of producing monthy (and hopefully weekly) emission estimates at 5-10 km resolution. Although capable of being applied to all emissions, it is most suitable for use in estimating agricultural emissions as it has the potential to look at the effects of individual events (e.g., slurry spreading, rain) on emissions.

To achieve this a network of four new instruments measuring the atmospheric concentration of methane will be established in East Anglia, in addition to one supported by DECC. There are two reasons East Anglia is chosen for the pilot project: (i) the land is flat and so the quality of the meteorological information is higher than for other terrains; (ii) it is logistically easier to manage from Cambridge in terms of both the instruments and development of contacts in the local agricultural community. Methane is chosen as the target gas because the incremental methane changes resulting from agricultural emissions are larger and easier to detect than the incremental N2O changes. In addition, the network can be developed more cost-effectively. The network will cover a region about 100-150 km square with a range of emissions expected according to the UK National Emissions Inventory.

Using high resolution meteorological information available on a 1.5 km grid in the UK, the NAME Inversion system will be run in inverse mode to allow emissions estimates to be calculated. This high resolution information coupled with the hourly measurements of methane are expected to provide weekly emission estimates on a scale of 5-10 km. These estimates will be compared to other, larger-scale estimates that are available such as those from the DECC Greenhouse network. The results are capable of being further analysed in a number of ways, so higher spatial resolution information would be available if the data were averaged over a longer period. Alternatively, any day/night variations or the effects of rainfall, ploughing or slurry-spreading could be investigated and so provide some constraints on individual components in the emissions, and not just on the overall emission estimate.

This study will be used as a pilot project for the technique. If successful, the approach can easily be transferred to other regions and to include N2O as well as CH4. There is thus considerable potential to leverage additional funds through co-funding which could be used to extend the scope of the study and to develop opportunities to collaborate with other interested parties in agriculture as well as research groups who are estimating GHG emissions on larger scales. This will be the subject of a proposal to NERC later this year. A NERC PhD student is already due to start developing the analysis technique with NAME in October 2011.









Objective
7. (b) Objectives


The overall aim of this project is to develop a method to estimate atmospheric emissions of methane using atmospheric measurements and the UK Met Office’s NAME Inversion system. This method will be capable of providing verification of the currently available national emission inventory in the regions where it is applied. It will be easily transferable to provide similar verification for nitrous oxide emissions.
The specific objectives are:
O1. Set up four gas chromatographs in the laboratory to measure methane with a precision of 1-3 ppb on an hourly basis (month 4);
O2. Install these instruments as a network in East Anglia (month 6);
O3. Make continuous measurements for 6 months (month 12);
O4. Provide estimates of emissions (month 24);
O5. Provide assessment of high resolution emissions technique (month 24);
O6. Compare emission estimates with estimates from national emissions inventory and larger scale studies (month 24).

Time-Scale and Cost
From: 2011

To: 2013

Cost: £100,395
Contractor / Funded Organisations
University of Cambridge
Keywords
Agriculture and Climate Change              
Climate Change